MENINGES PLAY A NEUROTROPHIC ROLE IN THE REGENERATION OF VASOPRESSIN NERVES AFTER HYPOPHYSECTOMY

Following hypophysectomy the regenerating fibers of magnocellular neur ons are known to establish new neurohemal connections with reorganized vasculatures in the median eminence, which lead to establishment of a posterior pituitary-like structure. In order to examine the role of t he meninges (the pia mater and the arachnoid) in this regeneration pro cess, we implanted the meningeal tissues obtained from neonatal rat pu ps into the third ventricle of the adult rats, and then hypophysectomi zed the host animals. Ten days after hypophysectomy, the meningeal tis sue grafts were found to be densely innervated by regenerating vasopre ssin-immunoreactive fibers. Such fibers had dots and frequently formed large punctuations. On the contrary, few vasopressin fibers were foun d within the cortical tissue grafts. Further, the exposure of primary hypothalamic cell cultures to the medium conditioned by meningeal cell cultures promoted not only the survival of vasopressin-immunoreactive neurons but also the outgrowth and arborization of the neurites. The survivals of cortical and cerebellum neurons in culture were also prom oted by the conditioned medium. These findings raise the possibility t hat the meninges play an important role in the axonal regeneration pro cess after hypophysectomy.